1、英文原文Destress Blasting in Coal Mining State-of-the-Art ReviewPetr Konicek1,* , Mani Ram Saharan2, Hani Mitri31Institute of Geonics Academy of Sciences of the Czech Republic,Studentska 1768, 708 00 Ostrava-Poruba, Czech Republic,2Central Institute of Mining & Fuel Research (CIMFR), Seminary Hills, Nag
2、pur, India,3McGill University, Montreal, Quebec, Canada H3A 2A7Abstract:Coal mine workings continue to face the challenges of coal bumps and rockbursts caused by high mining-inducedstresses due to high overburden pressures associated with the extraction of brittle, low strength coal seams. Despite o
3、fthe fact that destress blasting has been applied for almost a century, it is still not a popular choice. This paper presentsa state-of-the-art review of destress blasting in coal mining. Information such as geology, rock properties, miningconditions as well as blasting parameters such as blasthole
4、layout, hole length, explosive loading etc. are presented.The paper discusses the main benefits of destress blasting and the evaluation of its effectiveness as a measure toovercome the challenges of high mining-induced stresses causing coal bumps and rockbursts.Keywords: Mining, Coal,Destress Blasti
5、ng1. IntroductionIt is elementary but important to illustrate that an underground excavation initiates a process of reequilibrium,which leads to the generation of stresses around the excavation in a manner that free surfaces become planes for principal stresses and experience a bi-axial state of str
6、ess condition. The excavation boundaries may experience damage effects due to stresses and these effects for coal mines can be dislocation of rock reinforcement, interbed crossover of laminated roof rock mass, cutter failure, floor heave and/or rockburst/coal bump (Fig 1). These damaging effects are
7、 presented in the order of their severity according to the stress level, corresponding strength (uniaxial and poly-axial) at the point of consideration of the stress loading. Excess of the stress level in comparison to the strength and the rate at which the excess is attained during the re-equilibri
8、um process is manifested into the different damaging effects as illustrated in Figure 1. A faster rate in obtaining excess stresses will result into rockburst/coal bump. Occurrence of this excess stress over a greater area will increase the severity of the damaging effects. Further, part of the exca
9、vation experiences stress concentration and another experiences stress relaxation due to the shape of the opening and in situ stress directions.a bc dFig 1. (a) Rockbolt dislocation in an Indian coal mine; (b) Interbed crossover in a coal mine of South Africa 1; (c) Cutter roof failure in an US coal
10、 mine 2; (d) Rockburst in a German coal mine 3.Past research for measurement of stresses, understanding of stresses and prediction of the timing when and the rate at which the stresses will be in excess of the strength has been a mixed success. The mining process has, in the meantime, become faster,
11、 larger and being done at deeper levels. It is thus necessary that protective measures be evolved to deal with the damaging effects of excessive stresses. Figure 2 illustrates different methods evolved to deal with the damaging effects of excessive stresses and distress blasting is one of the oldest
12、 and proactive measures amongst the other methods 4. The mechanism of destress blasting is not well understood despite of the application of destress blasting in a wide range of mining conditions and objectives.The paper presents various conditions for which destress blasting is applied for deep coa
13、l mines and discusses the possibilities to further improve the method. The application of destress blasting is aimed into the zones of stress concentration in such a manner that the stress concentration zone shifted interior to the rock mass thus leaving a protective barrier between the work force a
14、nd the stress concentration zone. This mechanism of destress blasting is illustrated in Figure 3, which demonstrate that destress blasting shifts stress concentration zone away from the active working front.Fig. 2. Methods to reduce damaging effects of excessive stresses 4Fig. 3. Geomechanics effect
15、s of destress blasting 52. Natural and mining conditionsHardcoal deposits are mostly complex sedimentary sequences containing coal seams (multiseam deposits) in Upper Paleozoic age. Rocks between coal seams comprise shale, mudstones, siltstones, sandstones and conglomerates. Thickness of coal bearin
16、g strata ranges from hundreds to thousands of meters, whereas the thickness of coal seams varies from 1 to tens of meters. The feature most common where cutter roof failure or floor heave occurs is the presence of thinly laminated roof / floor. The feature most common to seams in which rockburst occur is the close proximity
